coding-puzzles-challenges/reverse_string_II.py at main · arjunnath/coding-puzzles-challenges · GitHub

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# 541. Reverse String II
# Easy
# Topics
# conpanies icon
# Companies
# Given a string s and an integer k, reverse the first k characters for every 2k characters counting from the start of the string.

# If there are fewer than k characters left, reverse all of them. If there are less than 2k but greater than or equal to k characters, then reverse the first k characters and leave the other as original.

# Example 1:

# Input: s = "abcdefg", k = 2
# Output: "bacdfeg"
# Example 2:

# Input: s = "abcd", k = 2
# Output: "bacd"

# Constraints:

# 1 <= s.length <= 104
# s consists of only lowercase English letters.
# 1 <= k <= 104


class Solution:
    def reverseStr(self, s: str, k: int) -> str:
        slist = list(s)
        slen = len(slist)
        i = 0
        j = k - 1
        ctr = 0
        while j < slen :
            while i < j :
                slist[i], slist[j] = slist[j], slist[i]
                i += 1
                j -= 1
            ctr += 2
            i = (ctr) * k
            j = i + k - 1
        if slen - i < k :
            j = slen - 1
            while i < j :
                slist[i], slist[j] = slist[j], slist[i]
                i += 1
                j -= 1
        return "".join(slist)

s = Solution()

test_strs = [
    ["abcdefgh", 2 , "bacdfeg"] ,
    ["abcdefg", 3, "cbadefg"] ,
    ["abcdijklpqrstuvwzonezone", 4, "dcbaijklsrqptuvwenozzone" ] ,
    ["abcdefg", 8, "gfedcba"]
]

for t in test_strs :
    print(f'input str : {t[0]}, k : {t[1]}, result : {s.reverseStr(t[0], t[1])}, expected : {t[2]}')